1. Field of the Invention
The present invention relates to an ice making machine including a refrigerating system equipped with a hot gas pipe.
2. Description of the Prior Art
Referring now to FIG. 5 of the accompanying drawings, which shows a refrigerating system and an icing water circulating circuit in a conventional automatic ice making machine of a water flow-down type, a high temperature and high pressure coolant discharged from a compressor 11 of the refrigerating system generally denoted by 10 is condensed when passing through a condenser 12 during an ice making cycle. The condensed coolant is expanded through an expansion valve 13 and evaporated within an evaporator tube 14 while depriving the icing water of heat to be subsequently fed back to the compressor 11. The icing water (i.e. raw material water to be formed into ice) is sprayed over the outer surfaces of ice forming plates 31 and 32 of an ice making unit 30 from a water circulating pipe 21 constituting a part of the water circulating circuit 20. In the course of circulation of the icing water as well as the coolant, the temperature of the former is lowered, ultimately resulting in ice pieces or pellets 1 being formed on the outer surfaces of the ice forming plates 31 and 32, as indicated by double dotted lines.
On the other hand, in the deicing operation cycle, a hot gas valve 41 installed in a hot gas pipe 40 is opened, whereby the high temperature and high pressure coolant (gas) discharged from the compressor 11 is directly introduced into the evaporator tube 14, while a water feed valve 27 communicated with an external water service system is opened to supply tap water between the ice forming plates 31 and 32. consequently, those portions of ice pieces 1, which are in contact with the outer surfaces of the ice forming plates 31 and 32, are heated and melted under the action of both the high temperature and high pressure coolant and the tap water supplied from the external water service system, allowing the ice pieces to drop within an ice storage box (not shown).
In the ice making cycle of the automatic ice making machine, the temperature and pressure of the coolant prevailing at the exit of the evaporator tube 14 and hence at the suction port of the compressor 11 are susceptible to the influence of ambient temperature. More specifically, the external conditions (such as the temperature of the icing water, the ambient temperature and others) for the evaporator tube 14 which extends through the ice making unit 30 undergo remarkable changes. In that case, the compressor 11 may be considerably overloaded, when the coolant is placed under a high pressure due to increased evaporation. Under these circumstances, the temperature and the pressure of the coolant are measured by means of a temperature sensor 13a (disposed on the exit end of the evaporator tube 14) and an external equalizer tube 13b so that the opening and closing of the external equalizer expansion valve 13 is controlled on the basis of the measurements.
In the case of the automatic ice making machine described above, the external equalizer expansion valve 13 is opened when the pressure of the coolant at the exit or outlet of the evaporator tube is relatively low.
With the arrangement as described above, the temperature of the coolant prevailing at the exit of the evaporator tube tends to become high when the high temperature coolant (gas) is supplied directly to the evaporator tube in the deicing or defreezing operation cycle. Besides, when the ambient temperature is lowered, the pressure within the refrigerating system becomes relatively low to such an extent that the temperature and pressure conditions for opening the expansion valve are satisfied. Thus, the expansion valve is opened notwithstanding the defreezing or deicing cycle. If such a situation occurs, low temperature liquid coolant may undesirably flow into the evaporator tube 14, whereby the defreezing operation for removing the ice pieces is rendered difficult or even impossible creating serious problems.